There is a need for new oral drugs to treat visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL). Our labs have discovered that several 2,4-diaminoquinazolines possess in vitro antileishmanial activity at low micromolar to high nanomolar concentrations, and one molecule in this series (KVH14) has shown promising efficacy in our murine model of VL. In this project, we will carry out focused lead optimization studies to identify quinazoline compounds that could serve as preclinical candidates for treating VL and/or CL. To this end, we propose the following aims: Aim 1: Synthesis of 2,4-Diaminoquinazolines with in vivo Antileishmanial Activity. Based on frontrunner compound KVH14, we will continue to conduct structure-activity and structure-property relationship (SAR and SPR) studies to enhance antileishmanial activity while maintaining or improving physicochemical properties. The optimization efforts will mainly focus on structural modifications on the quinazoline scaffold as well as the quinazoline's 2-, 4,- 5-, 6-, 7-, and 8-positions. Aim 2 Antileishmanial Evaluation of 2,4-Diaminoquinazolines. In vitro and in vivo assays to assess the potential of these molecules as drug candidates against both VL and CL will be conducted. Evaluation of the potency of these molecules against intracellular L. donovani (which causes VL), L. amazonensis (a species causing New World CL), and L. major (which causes Old World CL) will allow for the identification of molecules to be tested in murine models of VL (antileishmanial IC50 < 0.5 M and SI > 20) and CL (antileishmanial IC50 < 2 M and SI > 20). A hamster model of severe VL will also be used to discern whether a quinazoline showing outstanding oral efficacy in our murine VL model should be considered as a preclinical candidate for treating this manifestation of the disease. Aim 3. ADME/Tox Profiling of 2,4-Diaminoquinazolines. Metabolite identification for KVH14 and metabolic stability testing for active 2,4-diaminoquinazolines will be performed using mouse and human liver microsomes to inform our synthesis efforts in Aim 1 to enhance oral bioavailability and systemic exposure. Several development-limiting toxicities (i.e. hepatotoxicity, cardiotoxicity, and CYP3A4 inhibition will be evaluated for active 2,4-diaminoquinazolines to prioritize compounds for further testing. Pharmacokinetics and tissue distribution of the most promising 2,4-diaminoquinazolines will be determined in mice to verify plasma and target organ exposure.